JavaScript : 使用面向对象的技术创建高级 Web 应用程序
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记住这一点后,向对象添加方法将是很容易的事情:只需选择名称,然后将函数赋给该名称。因此,我通过将匿名函数分别赋给相应的方法名称,在对象中定义了三个方法:
var myDog = {
“name” : “Spot”,
“bark” : function() { alert(“Woof!”); },
“displayFullName” : function() {
alert(this.name + “ The Alpha Dog”);
},
“chaseMrPostman” : function() {
// implementation beyond the scope of this article
}
};
myDog.displayFullName();
myDog.bark(); // Woof!
C++/C# 开发人员应当很熟悉 displayFullName 函数中使用的“this”关键字 — 它引用一个对象,通过对象调用方法(使用 Visual Basic 的开发人员也应当很熟悉它,它在 Visual Basic 中叫做“Me”)。因此在上面的示例中,displayFullName 中的“this”的值是 myDog 对象。但是,“this”的值不是静态的。通过不同对象调用“this”时,它的值也会更改以便指向相应的对象,如图 2 所示。
Figure2“this”随对象更改而更改
function displayQuote() {
// the value of “this” will change; depends on
// which object it is called through
alert(this.memorableQuote);
}
var williamShakespeare = {
“memorableQuote”: “It is a wise father that knows his own child.”,
“sayIt” : displayQuote
};
var markTwain = {
“memorableQuote”: “Golf is a good walk spoiled.”,
“sayIt” : displayQuote
};
var oscarWilde = {
“memorableQuote”: “True friends stab you in the front.”
// we can call the function displayQuote
// as a method of oscarWilde without assigning it
// as oscarWilde’s method.
//”sayIt” : displayQuote
};
williamShakespeare.sayIt(); // true, true
markTwain.sayIt(); // he didn’t know where to play golf
// watch this, each function has a method call()
// that allows the function to be called as a
// method of the object passed to call() as an
// argument.
// this line below is equivalent to assigning
// displayQuote to sayIt, and calling oscarWilde.sayIt().
displayQuote.call(oscarWilde); // ouch!
Tags:JavaScript 使用 面向
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